The background reference here is to be considered as exemplary and not limiting. A boiling water nuclear reactor contains dry tubes which extend from the bottom of the reactor vessel to just below the upper core support grid and provide a water-tight cavity within the vessel for the reactor in core nuclear flux detectors. The upper end of each dry tube includes a spring-loaded plunger which engages the bottom of the upper support grid. Experience has shown that some plungers are not fully engaged in the bottom of the upper core support grid, a malfunction normally traceable to weakening of the plunger spring. Replacement of the defective plunger spring in the dry tube is not possible while the tube is in the reactor, thus requiring removal and replacement of the dry tube as the only heretofore recognized method of achieving repair.
According to the present invention, a simplified method of repair is provided which allows continued use of existing dry tubes. The invention comprises the provision of an extension adapter for the upper end of the defective plunger, resulting, in effect, in elongating the plunger to the extent necessary to make up for its decreased effective length because of the failure of its original spring. The adapter extension may be easily installed between the existing plunger and grid while the dry tube remains in the reactor vessel, as by the use of remote tools and viewing aids.
It is a feature of the invention that the adapter is a self-contained unit that fits tightly over the upper or free end of the plunger and contains its own captive spring which exerts forces between the interior of the adapter and top of the plunger so as to supplement the effect of the original spring or to substitute its force for the old spring, depending upon the extent of weakening of the old spring. A still further feature of the invention is that the adapter spring is backed up by a retainer and the walls of the adapter are so configured as to enable installation of the spring and retainer within the adapter body while preventing accidental escape of the spring and retainer. The configuration of the adapter walls is also such as to effectuate engagement of lugs on the walls with a knob at the upper end of the plunger.
The foregoing and other significant features and advantages of the invention will become apparent from the ensuing disclosure of a preferred embodiment of the invention.